Sinuous springs have been widely used in seat spring assemblies for a long time. They were originally developed to provide a spring seat which was substantially less expensive than traditional coil springs but provided satisfactory comfort. Nevertheless, until recently, no one has disputed the fact that coil springs did provide a much more luxurious seat.
In the last ten years, or so, developments of Lawton H. Crosby have greatly improved the results obtained with sinuous springs. As a result of these developments and others, many more sinuous spring seat assemblies are being used.
Conventionally, sinuous seat spring assemblies comprise wood rail frames with a plurality of sinuous spring bands stretched between them. An alternative is the steel rail construction wherein steel channels, angle irons or plain bars replace the wooden rails. The present invention is concerned with rail attachment assemblies and rail constructions for attaching sinuous spring bands to steel rails.
Steel rails are presently used primarily in heavyduty industrial, aviation, automotive, institutional and theater seating arrangements where the need for luxury, comfort, or noiselessness in minimal. In these cases, it is sufficient to merely attach the ends of the sinuous spring bands directly to the rails.
In residential furniture, however, a much higher level of luxury is desirable, if not required, and there must be no noise whatever. In other words, softness and resiliency are vital, not only at the center of the spring bands but also at the front and back rails.
The use of links providing radial, articulated action between the spring band ends and the front and back rails is the best way to get softness, resiliency and what is known in the trade as "deep-drop", a luxurious sinking in to the seat while still having substantial support. However, the conventional provision of apertures in the steel rails by punching, or forming of certain portions of the rail to form hooks, does not permit the use of radial action links or spring-ends into such apertures in residential furniture because such attachment means could not and does not hold the base segment of the link or spring against uncontrolled vertical and lateral motion as the spring band flexes and the link or spring-end moves up and down. Such uncontrolled motion causes unacceptable grinding and squeeking noises. This uncontrolled vertical or lateral motion and travel of the link or spring-end is referred to herein as "wandering".
In addition, where the rails are apertured, the apertures required must be relatively large to receive the spring ends. If relatively large apertures are punched for each of the large number of springs utilized in a normal sized sofa, for example, a dangerous weakening of the rail can result. Such is not the case in commercial seating, of course, where the number and span-lengths of springs are greatly reduced and the depth of deflection substantially less.